At present a Physical Hybrid Automatic Repeat Request (HARQ) Indicator Channel (PHICH) in a Long Term Evolution (LTE) Release 10 (Rel-10) system is relevantly defined as follows:
A PHICH is configured to carry Acknowledgement/Non-Acknowledgement (ACK/NACK) feedback information of an uplink service. A resource location of the PHICH is typically indicated by a parameter pair (nPHICHgroup, nPHICHseq) wherein nPHICHgroup represents the serial number of a PHICH group, and nPHICHseq represents the index of an orthogonal sequence.
The PHICH group conceptually refers to a set of Resource Elements (REs) in which 8 PHICHs can be transmitted and the PHICHs are respectively distinguished from each other by orthogonal sequences. There are 8 orthogonal sequences in case of normal Cyclic Prefix (CP), and then there are 8 PHICHs in one PHICH group; and there are 4 orthogonal sequences in case of extended Cyclic Prefix (CP), and then there are 4 PHICHs in one PHICH group.
Typically the number of PHICH groups in the LTE Rel-10 system can be determined as follows:
In a Frequency Division Duplexing (FDD) system, the number of PHICH groups is fixed in all of sub-frames and determined by Formula 1 below:
                              N          PHICH          group                =                  {                                                                      ⌈                                                            N                      g                                        ⁡                                          (                                                                        N                          RB                          DL                                                ⁢                                                  /                                                ⁢                        8                                            )                                                        ⌉                                                                              for                  ⁢                                                                          ⁢                  normal                  ⁢                                                                          ⁢                  cyclic                  ⁢                                                                          ⁢                  prefix                                                                                                      2                  ⋆                                      ⌈                                                                  N                        g                                            ⁡                                              (                                                                              N                            RB                            DL                                                    ⁢                                                      /                                                    ⁢                          8                                                )                                                              ⌉                                                                                                for                  ⁢                                                                          ⁢                  extended                  ⁢                                                                          ⁢                  cyclic                  ⁢                                                                          ⁢                  prefix                                                                                        Formula        ⁢                                  ⁢        1            
Wherein NPHICHgroup represents the total number of PHICH groups, Ngε{1/6,1/2,1,2} is configured by a high layer, NRBDL represents a system bandwidth, and the serial number of the index nPHICHgroup ranges from 0 to nPHICHgroup−1.
In a Time Division Duplexing (TDD) system, the number of PHICH groups may vary in respective downlink sub-frames and be given by mi·nPHICHgroup, wherein mi is determined by configuration information as depicted in Table 1, nPHICHgroup is calculated by the above Formula 1, and the serial number of the index nPHICHgroup ranges from 0 to mi·NPHICHgroup−1.
TABLE 1(A definition of factor mi)Uplink-downlinkSub-frame number iconfiguration012345678021———21——101——101——200—1000—1310———0001400——00001500—000001611———11——
Typically network side maps PHICHs onto Resource Element Group (REG) in a control region where Physical Downlink Control Channel (PDCCH) is located, and the REG is unused by Physical Control Format Indicator Channel (PCFICH) and Cell-Specific Reference Signal (CRS), a duration time of the mapping in time domain can be configured and broadcast by the system. Referring to FIG. 1, in a case of a normal PHICH time domain resource configuration (i.e., a Normal PHICH Duration), PHICHs are mapped onto a first Orthogonal Frequency Division Multiplexing (OFDM) symbol of a downlink sub-frame to support a scenario with a smaller number of users and a small coverage; while in a case of an extended PHICH time domain resource configuration, each PHICH group can be mapped onto the first 3 OFDM symbols of a downlink sub-frame; and in an especial case, each PHICH group can be mapped onto the first 2 OFDM symbols in a Multimedia Broadcast multicast service Single Frequency Network (MBSFN) sub-frame and TD-SCDMA Long Term Evolution (TD-LTE) sub-frames 1 and 6 to support a scenario with a larger coverage radius or a larger number of users. Furthermore, the number of PHICH groups in a cell can also be configured at 4 different levels (i.e., Ngε{1/6,1/2,1,2}), and the configuration situations are broadcast by the system to support various user capacities.
3 REGs occupied in the control region by one PHICH group are distributed differently in time and frequency domains for the purpose of maximizing time and frequency diversity gains. As illustrated in FIG. 1, FIG. 1 illustrates a schematic diagram of mapping resources of one PHICH group and shows that time-frequency resources occupied by one PHICH group are related to the number of REGs, a cell ID, the serial number of the PHICH group, specific serial numbers of OFDM symbols, etc.
Correspondingly, for a User Equipment (UE), when the UE transmits uplink data based on Physical Uplink Shared Channel (PUSCH), ACK/NACK feedback information corresponding to the uplink data is transmitted by the network side to the UE based on a PHICH in a downlink sub-frame, wherein considering a PUSCH transmitted in a sub-frame n, the UE receives a corresponding PHICH in a sub-frame n+kPHICH, and for a FDD system, kPHICH=4, and for the TDD system, kPHICH is determined through configuration information depicted in Table 2:
TABLE 2(A kPHICH configuration of a TDD system)TDDUL/DLUL sub-frame index nConfiguration0123456789047647614646266366646656646647
A specific location of a time-frequency resource occupied in a downlink sub-frame by a PHICH is decided jointly by a lowest PRB serial number among PUSCH resources indicated by scheduling signaling carried in Downlink Control Information (DCI) transmitted in the format 0 on PDCCH and a De-Modulation Reference Signal (DMRS) indicated by 3 bits.
A specific location of a time-frequency resource occupied by a PHICH is identified by a pair of parameters (nPHICHgroup, nPHICHseq) wherein nPHICHgroup represents the serial number of a PHICH group; and nPHICHseq represents the serial number of an orthogonal sequence in the PHICH group, particularly calculated by Formula 2:nPHICHgroup=(IPRB_RA+nDMRS)mod nPHICHgroup+IPHICHnPHICHgroup nPHICHseq=(└IPRB_RA/nPHICHgroup┘+nDMRS)mod 2NSFPHICH  Formula 2
Wherein nDMRS represents the value of a cyclic shift of a DMRS used in PUSCH corresponding to a PHICH and indicated by cyclic shift information in a DMRS field in the DCI format 0 (i.e., DCI in the format 0), and the specific mapping relationship is illustrated in Table 3.
TABLE 3(Mapping relationship between nDMRS and a cyclicshift for a DMRS field in the DCI format 0)Cyclic Shift for DMRS Field inDCI format 0 in [4]nDMRS00000011010201131004101511061117
Referring to a PUSCH transmitted in a sub-frame n, if there is no corresponding uplink scheduling instruction in the DCI format 0 or transmission of the PUSCH is scheduled by a random access response, nDMRS is set to 0;
NSFPHICH represents the size of a spreading factor for modulation of a PHICH defined in the standard 36.221;
      I    PRB_RA    =      {                                        I            PRB_RA            lowest_index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                in                                            ⁢                                                                                                                                                                                  ⁢                                            a                                            ⁢                                                                                                                                                                                  ⁢                                            case                                            ⁢                                                                                                                                                                                  ⁢                                            that                                            ⁢                                                                                                                                                                                  ⁢                                            a                                            ⁢                                                                                                                                                                                  ⁢                                            PDCCH                                            ⁢                                                                                                                                                                                  ⁢                                            indicates                                            ⁢                                                                                                                                                                                  ⁢                                            to                                            ⁢                                                                                                                                                                                  ⁢                                            schedule                                                                                    ⁢                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              ⁢                                                                                                                                    a                                              ⁢                                                                                                                                                                                          ⁢                                              first                                              ⁢                                                                                                                                                                                          ⁢                                              transmission                                              ⁢                                                                                                                                                                                          ⁢                                              block                                              ⁢                                                                                                                                                                                          ⁢                                              in                                              ⁢                                                                                                                                                                                          ⁢                                              a                                              ⁢                                                                                                                                                                                          ⁢                                              PUSCH                                                                                        ,                                                                                          or                                              ⁢                                                                                                                                                                                          ⁢                                              there                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          ⁢                                                                          is                                      ⁢                                                                                                                                                          ⁢                                      no                                      ⁢                                                                                                                                                          ⁢                                      corresponding                                      ⁢                                                                                                                                                          ⁢                                      PDCCH                                      ⁢                                                                                                                                                          ⁢                                      and                                      ⁢                                                                                                                                                                                                        ⁢                                                                                                                                                                                                      ⁢                                      the                                      ⁢                                                                                                                                                          ⁢                                      number                                      ⁢                                                                                                                                                          ⁢                                      of                                                                                                                                                                                                                                                                                                                              received                              ⁢                                                                                                                          ⁢                              NACKs                              ⁢                                                                                                                          ⁢                              is                              ⁢                                                                                                                          ⁢                              unequal                              ⁢                                                                                                                          ⁢                              to                              ⁢                                                                                                                          ⁢                              the                              ⁢                                                                                                                          ⁢                              number                              ⁢                                                                                                                          ⁢                              of                                                                                                                                                                                                                              transmission                        ⁢                                                                                                  ⁢                        blocks                        ⁢                                                                                                  ⁢                        in                        ⁢                                                                                                  ⁢                        a                        ⁢                                                                                                  ⁢                        PUSCH                        ⁢                                                                                                  ⁢                        recently                        ⁢                                                                                                  ⁢                        scheduled                                                                                                                                                                  by                  ⁢                                                                          ⁢                  a                  ⁢                                                                          ⁢                  PDCCH                                                                                                                    I              PRB_RA              lowest_index                        +            1                                                                                                                                          in                      ⁢                                                                                          ⁢                      a                      ⁢                                                                                          ⁢                      case                      ⁢                                                                                          ⁢                      that                      ⁢                                                                                          ⁢                      a                      ⁢                                                                                          ⁢                      PDCCH                      ⁢                                                                                          ⁢                      indicates                      ⁢                                                                                          ⁢                      to                      ⁢                                                                                          ⁢                      schedule                                        ⁢                                                                                                                                                                                                                                                ⁢                                          a                      ⁢                                                                                          ⁢                      second                      ⁢                                                                                          ⁢                      transmission                      ⁢                                                                                          ⁢                      block                      ⁢                                                                                          ⁢                      in                      ⁢                                                                                          ⁢                      a                      ⁢                                                                                          ⁢                      PUSCH                                                                                            ⁢                                                                    
IPRB_RAlowest_index represents a lowest PRB serial number allocated by a first timeslot in transmission of a corresponding PUSCH:
nPHICHgroup represents the number of PHICH groups, configured by high-layer signaling; and
      I    PHICH    =      {                            1                                                                                                          when                    ⁢                                                                                  ⁢                    TDD                    ⁢                                                                                  ⁢                    UL                    ⁢                                          /                                        ⁢                    DL                    ⁢                                                                                  ⁢                    is                    ⁢                                                                                  ⁢                    configured                    ⁢                                                                                  ⁢                    to                    ⁢                                                                                  ⁢                    be                    ⁢                                                                                  ⁢                    0                                    ,                  and                                                                                                                          a                    ⁢                                                                                  ⁢                    PUSCH                    ⁢                                                                                  ⁢                    is                    ⁢                                                                                  ⁢                    in                    ⁢                                                                                  ⁢                    a                    ⁢                                                                                  ⁢                    sub                    ⁢                                          -                                        ⁢                    frame                    ⁢                                                                                  ⁢                    of                    ⁢                                                                                  ⁢                    n                                    =                                                            4                      ⁢                                                                                          ⁢                      or                      ⁢                                                                                          ⁢                      n                                        =                    9                                                                                                            0                                      under            ⁢                                                  ⁢            other            ⁢                                                  ⁢            conditions                              
The foregoing relevant definition of a PHICH is currently applicable only to the LTE-Rel-10 system. A traditional method of providing an access with use of the single-layer coverage by a macro base station has failed to satisfy a user demand along with an increasingly growing data rate and demand for service load. Thus it is typical at present to address the foregoing issue by a hierarchical coverage, for example, some low-power base stations, e.g., a Home eNodeB/a pico base station/a femto base station/a relay base station, etc., are deployed in a hotspot area or indoors. Such a low-power base station is a base station device applied in a home indoor environment, an office environment or other hotspot small-coverage environment to enable an operator to provide an appealing service at a higher data rate and a lower cost. However the femto base station limits the accessing member users to a certain degree and is inaccessible to a non-member user, and if the non-member user enters the coverage area of the base station, then it may enter a coverage hole due to a stronger signal of the low-power base station and consequentially cannot operate. Moreover the pico base station at the same frequency as the macro base station may also generate strong interference and consequentially cannot operate. In order to address such interference, an existing practice is to set an Almost Blank Subframe (ABS), so that the base station transmits signals less frequently in the ABS so as to reduce interference to an adjacent cell, to perform Inter-Cell Interference Coordination (ICIC) through Time Division Multiple (TDM).
However in the existing TDM ICIC mechanism, the interfering base station configured with the ABS will not transmit any control information in the ABS in order to avoid interferences, so transmission of a PHICH in the control region may be limited due to the introduced ABS mechanism.
On the other hand, the definition of an extended carrier may be introduced to the LTE Rel-11 system, that is, a PDCCH control region supported in the LTE Rel-10 system is not included in an extended carrier, but a PUSCH can be scheduled in an extended carrier, and thus other compatible component carriers are scheduled through cross-carrier scheduling on one hand, and transmission of an enhanced PDCCH can be newly defined over an extended carrier on the other hand, wherein a PDSCH transmission region is occupied for transmission of an enhanced PDCCH. Thus limited transmission of a PHICH in the control region may also arise in the latter case.
In the prior art, a method to address the issue of limited transmission of a PHICH is to adopt scheduling signaling in the DCI format 0 for the system instead of a PHICH to notify the UE whether to retransmit a PUSCH, but this method may result in an extra overhead of system signaling and a consequential increase in operation load of the system, thus degrading the performance of the system.